The true Temple is St. Peter's Basilica that's built over the burial site of St. Peter in Rome.
Scripture and prophecy tells us the abomination of desolation will stand in the Temple (the true Temple of God, not a false temple that will be built in Jerusalem), shewing himself as if he were "god".
It's seems clear that the Antichrist will usurp Rome according to the Scriptures and what's been happening since Vatican II Council.
Just as God destroyed the first two Temples of Solomon and Herod II, respectively, for the sins and faithlessness of the early Hebrews, He will destroy the third Temple which is seized by Antichrist, for the sins and faithlessness of Catholics (the true Jєωs). We see a parallel here that God destroys His Temples used by His children who once held the Faith, but have apostatized. This doesn't mean the Catholic Church will be destroyed.
Many people mistakenly think the Antichrist's temple will be in Jerusalem because the Antichrist Jєωs will be building another temple there for their false messiah, but Scripture tells us he will stand in the actual Holy Temple of God. This can only be the Temple of the Catholic Church.
Numerous verses in Scripture point to St. Peter's Basilica in Rome as being Babylon, which even the Apostles themselves referred Rome (the physical center point of the Church) as being Babylon. Scripture also tells us Babylon, which is the Vatican, will fall during the Apocalypse.